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Author Topic: 18650 charger burned out....what'd I do?!  (Read 3885 times)

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Offline Master Valon

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18650 charger burned out....what'd I do?!
« on: August 05, 2013, 07:38:20 PM »
Hey there, I just made a circuit for a 501st member's Jawa eyes, so I picked up one of the $5 single 18650 chargers to give them. I went to go charge the 3400mAh protected 18650 I got for the circuit, and it started to charge normally. Then about 5 minutes into charging, I hear a "POP" and I look and the charging LED was out, so I rushed over to unplug it and get the cell out. The cell was only a tad warm, I don't even know if it was warmer than when I put it in the charger. But the charger itself was very warm, in parts, I'd say it was hot. Also, it definitely smelled like something had burned out internally. Now, I'd regularly assume it was just a bad charger, and that it was no biggie, because they are so cheap. BUT...When I was making the circuit, the cell fit very, very tightly in the battery holder, and when I pushed it in once, the button tab-thing on the positive side of the cell slid partially off the cell. I popped it out, and saw that the metal button top was connected to the positive terminal on the cell by a ribbon-like tab. That tab also ran to the negative terminal under the shrink wrap. I couldn't reaffix the button tab, so after assessing it as just there to make a tighter fit (as on unprotected cells, there is not button head). So after some deliberation, I cut off the button head. The cell fit much better in the holder, lit up the LEDs, etc. So I thought it was all good. But then the whole charger thing happened, so I am unsure if it was just a faulty charger, or if by removing the button tab, I altered the protection circuit in the cell and caused the charger to give it too much current when charging. I tested the cell, and the PCB wasn't tripped, because it still powers the LEDs. Any idea of what went wrong, and if that cell is still safe to use?
Though this is the end of the age of heroes, it has saved its best for last.

Offline erv

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Re: 18650 charger burned out....what'd I do?!
« Reply #1 on: August 08, 2013, 10:57:21 PM »
I got a trustfire charger to die like that with no reason

To test the cell, I would discharge it slowly in a 5 mm LED + resistor (@20 mA) for a while, then try to recharge it again with another charger, under monitoring, then check temp, and finally, if charged "correctly" (charger goes green) measure with DMM the voltage which should be in the ballpark of 4.2-4.3V and not more.
That would indicate the PCB is still working correctly.
Then another discharge to see if the PCB cuts at the right moment.

Offline Master Valon

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Re: 18650 charger burned out....what'd I do?!
« Reply #2 on: August 08, 2013, 11:29:37 PM »
Alright, thanks for the tip, erv. I think the guy I made the circuit for is picking it up this Sunday, though, so just to be safe, I'll order another cell and charger for him, so I can be sure it's all good. Then when I have more time I'll test the cell I have (I don't have a 5mm LED or proper resistor, OR DMM, so I'd have to go and buy them at RadioShack). Just out of curiosity, do you know if the button head on protected 18650s are wired in with the PCB at all? If not, what purpose do they serve?
Though this is the end of the age of heroes, it has saved its best for last.

Offline erv

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Re: 18650 charger burned out....what'd I do?!
« Reply #3 on: August 11, 2013, 06:37:14 PM »
the positive of the battery is also going to the PCB, usually located at the bottom of the cell on the negative.
A double cell pack must be wired with a dual-cell PCB with a middle point, wiring 2 individually protected cells in series is a bad battery pack design as it creates unbalanced packs after only a short time / small number of recharge operations.

Offline Master Valon

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Re: 18650 charger burned out....what'd I do?!
« Reply #4 on: August 11, 2013, 07:06:15 PM »
Yeah, I understand about the 2 cell pack. I'm not trying to make one, though, sorry if I communicated that ineffectively. I was just wondering if the metal button head-tab thing that's on protected cells was essential to the PCB circuitry in any way. The positive terminal is still wired to the negative side and, I'm assuming, the PCB, with that ribbon-like tab. It's just the button top that I removed, so now the positive terminal is flat, as on an unprotected cell.

edit: This is what I'm talking about.

This button head, like on this:

http://www.orbtronic.com/images/products/borb-31.jpg

Compared to flat, on this:

http://www.nitemods.com/images/medium/_MAG_DLG_ICR_unprotected_18650_2200mAh_PTJ_MED.JPG

I have a protected cell, so the positive looked like the first image. Now, it's like the second. Other than that, no tampering has been made.
« Last Edit: August 11, 2013, 07:09:19 PM by Master Valon »
Though this is the end of the age of heroes, it has saved its best for last.

Offline PhoenixJedi

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Re: 18650 charger burned out....what'd I do?!
« Reply #5 on: August 11, 2013, 07:56:22 PM »
No, it shouldn't be.

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Offline Sunrider

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Re: 18650 charger burned out....what'd I do?!
« Reply #6 on: August 11, 2013, 08:11:20 PM »
 It sounds like an electrolytic cap blew in the charger. You could open it and see. It would be visibly burnt. A $15 charger can be junk, so a $5 charger may not even be worth trying to fix.

 It is also good practice to plug the charger in first then put the battery on to charge.

Offline Master Valon

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Re: 18650 charger burned out....what'd I do?!
« Reply #7 on: August 11, 2013, 08:27:30 PM »
Okay, cool, thanks you guys. Glad to have so many experts here on FX! Unfortunately, Sunrider, I don't think the charger survived my room cleaning purge this weekend, meaning I threw it away, so I can't check to see if that part was burned. Although, I smelled the charger after I removed the cell (I began doing that after I detected a shorted alkaline cell only after noticing the smell, haha) and it reeked of short circuit/burnt out-ness. I definitely burned out some component of the charger, but my uncertainty lies with how. I wasn't sure if the charger was just a lemon, or if I had rendered the PCB on the cell useless, and had caused the charger to overcharge the cell somehow. After what you, PJ, and erv have said, plus the fact that the PCB on the cell wasn't even tripped, I think it's safe to say the cell is okay to use, right? I've ordered a replacement charger and a few extra cells, but I did that with my own cash, as to not bug the guy I'm building it for to provide me with more $$$, so I didn't have much to spend...long story short, I had to settle for some UltraFire cells ( :/ ) and another cheap charger, so here's hoping this charger works okay.

Edit: Oh, and Sunrider- yes, that's how I always charge my cells. I plugged in the charger before putting the cell in.
Though this is the end of the age of heroes, it has saved its best for last.

 

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